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Double Bass Variable input impedance for DB amplification
- Thread starter Chris Fitzgerald
- Start date
Those would be the perfect 4 knobs to put on an effects pedal ever! Impedance, Phase, HP filter, and Volume... the perfect input device. I personally don't care about EQ, because that could be added later in the chain, either with a dedicated unit or by running through the native EQ circuit of the amp in question. But an input device like that would make traveling a lot less scary, and while at home I would find a way to mount in on my combo so I didn't have to mess with it on the gig other than to tweak the HP filter now and again.
As long as we're dreaming, if Tesla made a small SUV and gave me one for free, that would be cool too.
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Those would be the perfect 4 knobs to put on an effects pedal ever! Impedance, Phase, HP filter, and Volume... the perfect input device. I personally don't care about EQ, because that could be added later in the chain, either with a dedicated unit or by running through the native EQ circuit of the amp in question. But an input device like that would make traveling a lot less scary, and while at home I would find a way to mount in on my combo so I didn't have to mess with it on the gig other than to tweak the HP filter now and again.
As long as we're dreaming, if Tesla made a small SUV and gave me one for free, that would be cool too.
Tesla does indeed make a SUV you’d also need a solar pannel array on your roof to charge it.
Ric
A device for Double Bass with HPF and variable input impedance from 1 Meg Ohm to 10 Meg Ohm would be great!. There is a big need of a preamp or box designed for live bass with variable input impedance with that range
The Clarus SL has both high and low impedance inputs. And HPF. But, not variable inputs so I guess it's not exactly what you want.
Many amps have 2 impedance settings like the Clarus (1 meg ohm and 10 megohm, some others even more), This is not what I want at all. and I am happy with the amp I use (tecamp puma 1 megohm input).
I use and like the Full Circle pickup and what I don't like about the PZB input ("piezo optimized") on the Radial Bassbone V2 is that the switch increases impedance to 10 meg-ohms AND gain by 10dB, making the sound so hot and in your face that its practically unusable, with the added complication that its harder to match or balance volumes when playing a doubling gig with an electric bass on the other channel. So again, just like a lot of studio gear, variable input impedance (not fixed settings) from 1 Meg Ohm to 10 Meg Ohm would be great on a device designed for Live bass.
Apparently, this just isn't practical or no ones done it. The Felix has three fixed input impedance settings, so does the Headway EDB-2. I'm not fond of 10 Meg Ohm's either but I'm using an Ehrlund EAP and their preamp is set somewhere around 2 Meg Ohms.
So either the Felix or the Headway work just fine.
Ofcourse, there is this: Invalid Link Removed
Edit: Oh sorry, the variable impedance is in the bassguitar range... I just seemed to remember there is a device with this feature...
There is this: Summit Audio - TD-100 Features. But only goes to 2 Mohms. Otherwise fascinating, if it went to 10 Mohms, had phantom power and perhaps a hpf...
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There was a TB get together where folks tried the Summit Audio box out, but as you mentioned it’s missing some things. Both the Felix and EDB-2 work very well. One is less expensive.
A variable impedance is not very practical in the long run, because the pot will oxidize and crackles will occur or even no sound or a very quiet and probably distorted one.
There are hardly any regular pots that have 10 MegOhms, I found some trim pots with 5 MegOhms, but nothing higher yet.
But you do not need continuously adjustable impedance, just a lot of steps.
A circular switch with about ten positions and ten 1 MegOhms resistors in series with a connection to one of the switch steps can give you 1 MegOhms steps. The first goes to the hot instrument/FET input and the switch wiper goes to the ground. Replace the input easiest or from hot instrument/FET input to ground.
It's basically a quantized pot. The switch won't oxidize as badly as a pot and since the Headway and the Felix have switches for input impedance it should not be worse than these ones.
Using a geometric progression of resistor values gives a better characteristic of switch positions, but they would be harder to calculate and select from the typical values, so the arithmetic progression (constant 1 MegOhms steps) is OK if you don't want to go the more complicated route.
I'm rather sure Francis Deck can make that as a custom mod to one of his HPFpre's if there is enough room in the enclosure.
There are hardly any regular pots that have 10 MegOhms, I found some trim pots with 5 MegOhms, but nothing higher yet.
But you do not need continuously adjustable impedance, just a lot of steps.
A circular switch with about ten positions and ten 1 MegOhms resistors in series with a connection to one of the switch steps can give you 1 MegOhms steps. The first goes to the hot instrument/FET input and the switch wiper goes to the ground. Replace the input easiest or from hot instrument/FET input to ground.
It's basically a quantized pot. The switch won't oxidize as badly as a pot and since the Headway and the Felix have switches for input impedance it should not be worse than these ones.
Using a geometric progression of resistor values gives a better characteristic of switch positions, but they would be harder to calculate and select from the typical values, so the arithmetic progression (constant 1 MegOhms steps) is OK if you don't want to go the more complicated route.
I'm rather sure Francis Deck can make that as a custom mod to one of his HPFpre's if there is enough room in the enclosure.
So the question that I keep coming back to after reading a bunch of threads containing info about input impedance is this:
If higher input impedance is really the best for all sources, why do so many units - from mic preamps to instrument preamps to combo amps - offer a choice of input impedance settings? Heck, even my ancient Polytone amp had a Hi and Low input choice. If higher is always better, why bother with low at all?
EDIT: Double MIDI - when i use the HFPre, I put it in the FX loop, so either way the whole circuit is being used, just in different order.
Were those were hi/lo impedance inputs or hi/lo level inputs?
In general, with input impedances you want them to be high enough to not cause loading to the output of the device you are plugging in to that input.
But you don’t want it so high that it makes the connection between the instrument and the amp more susceptible to noise or cable capacitance effects.
So yes, there may be a sweet spot but it is more dependent on what is being plugged into the amp than the amp itself. If you have both a hi and lo impedance input that would allow the use of equipment that has either hi or low impedance requirements.
Again, I speak in general. How this might apply to your situation can have other variables.
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It might be that the loading (input impedance of the following circuit) has an influence on the mechanics of the piezo crystal.
A high input impedance is a low load to the crystal and that might (!) let the crystal resonate almost undamped on some of its eigenfrequencies which might be the reason for the piezo quack sound. A lower input impedance means a higher load to the crystal, so the energy goes out more in the electric current rather than keeping it in mechanic resonance.
We shouldn't forget that a piezo is a electromechanical transducer that works in both directions. That piezo disk we all know from car buzzers or music greeting cards is the same that some manufacturers use for pickups.
So if electrical energy produced by mechanical stress is not consumed completely by the electric current flow, some of it might get reflected back to mechanical energy.
But this is more (informed?) speculation. I'm pretty sure some of that is true to some point, but I would be happy to get corrected by more informed members here.
A high input impedance is a low load to the crystal and that might (!) let the crystal resonate almost undamped on some of its eigenfrequencies which might be the reason for the piezo quack sound. A lower input impedance means a higher load to the crystal, so the energy goes out more in the electric current rather than keeping it in mechanic resonance.
We shouldn't forget that a piezo is a electromechanical transducer that works in both directions. That piezo disk we all know from car buzzers or music greeting cards is the same that some manufacturers use for pickups.
So if electrical energy produced by mechanical stress is not consumed completely by the electric current flow, some of it might get reflected back to mechanical energy.
But this is more (informed?) speculation. I'm pretty sure some of that is true to some point, but I would be happy to get corrected by more informed members here.
Good point. Many amplifiers have HI and LOW level inputs. I believe those were put there to accommodate active bass guitar with powered preamps. With
the exception of the Mark Bass Big Bang and the Markbass Nano (set at 2) and the Phil Jones Suit Case, Flight Case, and Super Flight Case (set at 4 Meg Ohms)
Most other amps are set at 1 Meg Ohm.
Old thread revival.
Wondering how useful the variable impedance would really be…
Did anyone get one of those Broughton units with the variable input and HPF?
Wondering how useful the variable impedance would really be…
Did anyone get one of those Broughton units with the variable input and HPF?
Azure Skies
Commercial User
I made a small batch, and they were pretty slow to sell. I've had a few dozen requests to bring it back, not sure if that's quite enough to bring it back. So far I've had great success just offering a fixed customizable input resistance for my preamp/filter pedals. I think it's too much to think about for a lot of musicians, so a fixed input works fine for a lot of people. I've probably sold at least 10x the amount of custom input resistance HPFs as I did variable resistance HPF-DI. Who knows, maybe the demand would be there today.
Thanks for the info. Did you ever get any feedback as to how much varying the input resistance affected the tone?
I’ve been using an FDeck, which is 10M, I think. It’s nice because I can just Velcro it to my tailpiece. My thoughts are to warm up or tube-ify the tone before hitting the SS combo amp.
Azure Skies
Commercial User
The only thing I remember is a number of players saying they were surprised they actually preferred a lower input impedance than they would have thought. A lot of them landed at 2 or 3 meg. The most common input impedance request I get is 5 meg, so I'm thinking the 10 meg might be too high for a number of people. Totally depends on your pickup, though.
That's certainly what I use with either a Realist Life Line or the Ehrlund EAP. Both the Headway EDB 2 and the Grace Designs Felix have settings that circle or select the 5 Meg Ohm setting. Rick at Acoustic Image did some testing a few years ago
and found that the Fishman BP 100 was the only piezo pickup they tested, that really benefited from 10 Meg Ohm. That's probably the primary reason that the Fishman Pro Platinum Pre had a 10 Meg Ohm input impedance. Just my take of course
Tesla does indeed make a SUV you’d also need a solar pannel array on your roof to charge it.
Ric
I've got the solar panel array; they power the house and the shop. I'm just waiting on the free Tesla....
